This invention is directed to apparatus, and to the method for crimping and sealing the end of a thin walled, inflexible plastic tubing member, such as made from vinyl, PVC and the like, where such end preferably exhibits a uniquely configured end design in the shape of an arrowhead. An integral step of the method hereof includes the controlled heating of the end of such tubing member prior to crimping and sealing. While the invention has broad application, a particular use thereof may be the formation of a stake element for a picket fence, the design of which is illustrated in co-pending patent application, Ser. No. 479,038, filed Feb. 12, 1990, by one of the inventors hereof.
With the current and large use of plastic for containment applications, there is a quantity of information available on sealing flexible plastic film to form an enclosure. Less, however, is known about crimping and sealing a relatively rigid, thin walled plastic member as taught herein. In regard to thicker and more rigid plastic products, it is known to close plastic containers which are still in a hot state from the preceding fabrication process, such as a blowing process, by pinching the two opposite ends of the wall together by clamping jaws which also effect the welding together of these walls and the closing of the pouring aperture. Plastic containers which are no longer in a plastic or pliable condition are closed by supplying heat to the outer circumference of the aperture part or spout, for example, through clamping jaws which are used to pinch these walls together to thereby make the material of the container sufficiently plastic to cause a welding of the aperture when the clamping operation is effected. The heat requirement for sufficient plastisizing of the aperture part to be welded is relatively great. In addition, by means of the heating clamping jaws it is not possible to produce, in the aperture portion to be welded, a local weakening of the material which may be desired to form a tear line in order to facilitate the subsequent opening of the container by tearing along this line.
U.S. Pat. No. 3,765,144 to Schlesser et al teaches an improved method and apparatus to form a closure in a plastic container, for example. A critical feature thereof appears to be the use of a central heater, which enters into an aperture to heat opposite sides thereof, including means to heat the interior end, prior to flattening such end.
While the present invention is not preferably concerned with the formation of a container, it nevertheless is directed to sealing a plastic tubular member at at least one end thereof. It achieves the results through a method and apparatus that is not found in the prior art, nor in related art. The features of this invention will become more apparent from a reading of the following specification, particularly when read in conjunction with the several Figures.